What is one method of leak testing that involves the use of gas?

Helium mass spectrometer testing is a highly effective method for leak detection that specifically utilizes gas, making it the correct choice. In this process, helium is introduced into the system being tested. The helium is then allowed to escape through any potential leaks. Since helium is a light and inert gas, it can easily pass through minute cracks or holes that other gases might not escape from.

The advantage of this method is its sensitivity; helium can detect extremely small leaks more efficiently than many other gases or methods. A mass spectrometer is employed to identify and measure the concentration of helium that escapes, allowing for precise determination of leak points. This makes it particularly valuable in industries requiring high integrity systems, such as aerospace or nuclear applications.

Other methods mentioned, such as hydrostatic testing, involve the use of liquids rather than gases; a specific fluid is introduced to test the integrity of a system. Vacuum testing generally concerns the removal of air from a system rather than using gas to detect leaks. X-ray testing is primarily utilized for inspecting the internal structures of materials rather than identifying leaks. Thus, helium mass spectrometer testing stands out as the most relevant method for leak testing that specifically involves the use of gas.